bug #15721 [FrameworkBundle] compatibility with older Form component versions (xabbuh)

This PR was merged into the 2.8 branch.

Discussion
----------

[FrameworkBundle] compatibility with older Form component versions

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #15711
| License       | MIT
| Doc PR        |

Commits
-------

01ad767 compatibility with older Form component versions

src/Symfony/Bundle/FrameworkBundle/Controller/Controller.php

@@ -292,7 +292,16 @@ class Controller extends ContainerAware
      */
     public function createFormBuilder($data = null, array $options = array())
     {
-        return $this->container->get('form.factory')->createBuilder('Symfony\Component\Form\Extension\Core\Type\FormType', $data, $options);
+        if (method_exists('Symfony\Component\Form\AbstractType', 'getBlockPrefix')) {
+            $type = 'Symfony\Component\Form\Extension\Core\Type\FormType';
+        } else {
+            // not using the class name is deprecated since Symfony 2.8 and
+            // is only used for backwards compatibility with older versions
+            // of the Form component
+            $type = 'form';
+        }
+
+        return $this->container->get('form.factory')->createBuilder($type, $data, $options);
     }
 
     /**